In the field of producing printed wiring boards, photosensitive resin compositions have been widely employed as resist materials used for etching or plating. The photosensitive resin composition is often used as a photosensitive element (layered product) provided with a support and a layer which is formed on the support using the photosensitive resin composition (hereinafter, sometimes referred to as “photosensitive resin composition layer”).
For example, the printed wiring board is manufactured as follows. First, a photosensitive element having a support and a photosensitive resin composition layer is prepared, and the photosensitive resin composition layer of the photosensitive element is formed on a substrate for forming circuits (photosensitive layer forming process). Next, the predetermined area of the photosensitive resin composition layer is irradiated with active light rays to cure the exposed area (exposure process).
Then, the unexposed area is then removed (developed) from the substrate, thereby forming a resist pattern, which is the cured material of the photosensitive resin material (hereinafter, sometimes referred to as “resist cured product”), on the substrate (developing process). The resist pattern obtained is used for etching or plating to form a circuit on the substrate (circuit forming process), and finally the resist pattern is released and removed to manufacture a printed wiring board (releasing process).
As an method of exposure, a method in which exposure is carried out through a photomask using a mercury lamp as a light source is conventionally employed. Recently, an method of exposure called DLP (Digital Light Processing) or LDI (Laser Direct Imaging) has been proposed as a direct writing exposure method that allows direct formation of patterns without using a photomask based on digital data on the photosensitive resin composition layer. Such a direct writing method of exposure has improved alignment accuracy than the method of exposure through a photomask and allows the formation of finer patterns, and therefore increasingly used to manufacture substrates for high density package substrates.
In general, in the exposure process, the exposure time is desired to be reduced in order to improve the production efficiency. In the above direct writing method of exposure, however, monochromatic light such as laser is used as a light source and the substrate is irradiated with light rays while scanning. Therefore, the direct writing method of exposure tends to require a longer exposure time as compared to the conventional method of exposure carried out through a photomask. Accordingly, in order to reduce the exposure time to improve the production efficiency, it is necessary to improve the sensitivity of the photosensitive resin composition than the conventional one.
Meanwhile, in association with recent increase in density of printed wiring boards, the demand for a photosensitive resin composition that allows the formation of a resist pattern with sufficient resolution (resolution property) and adhesiveness is increasing. In particular, a photosensitive resin composition that allows the formation of a resist pattern having a L/S (line width/space width) of 10/10 (unit: μm) or less in manufacture of a package substrate is required.
In general, increase in resolution of the resist pattern is achieved by, for example, increasing the crosslink density after curing of the photosensitive resin composition. However, the resist pattern is hard and becomes fragile when the crosslink density in increased, and the problem of cracking of the resist pattern easily occurs in a conveyance process or the like. In order to solve this problem, the technique of increasing flexibility of the resist pattern is proposed. However, when the flexibility is increased, the resist pattern easily bends, which fact results in reduction in resolution property. Therefore, the features of increasing the resolution and flexibility are inconsistent with each other in the resulting resist pattern.
Moreover, in the developing process, it is necessary to shorten the time required for releasing the uncured photosensitive resin composition (sometimes referred to as “developing time”), so as to improve the production efficiency.
In order to meet these demands, various photosensitive resin compositions have been examined in the past. For example, a photosensitive resin composition in which the above required features are improved by using a specific binder polymer, a photopolymerizable compound, a photopolymerization initiator, and a sensitizing dye is disclosed in, for example, Japanese Patent Application Laid-Open (JP-A) Nos. 2005-301101, 2007-114452, and 2007-122028, and International Publication Nos. WO 08/07848, WO 10/098175, WO 10/098183, and WO 12/067107.